Combined Experimental and Numerical Investigation of Spray Propagation and Mixture Formation of Tailor-Made Fuels under Engine-Relevant Conditions

  Spray visualization WSA Visualizing the vapor phase of an engine-like fuel jet by Schlieren imaging: the liquid jet core is shown in black, surrounded by its vapor phase. The background displays the surrounding hot pressurized air.

Mixture formation quality is essential for engine performance and emissions. A qualitative experimental classification done in the first phase of this project has revealed the strong influence of the fuels’ thermophysical properties on mixture formation. In the future, this work will be extended by a more detailed quantitative analysis enabling the prediction of the temporal and spatial mixture formation process. The experimental methods selected are high-speed visualizations, offering phenomenological insight into the transient processes of spray propagation, and Phase Doppler Velocimetry for measuring the spray droplet behavior with high spatial and temporal resolution.

Although the experimental investigations of the first phase have provided valuable data regarding the fuel influence on mixture formation, experiments are not applicable for studying the influence of specific fuel properties independently, since all relevant properties are coupled (e.g. an increasing liquid density leads to an increasing liquid viscosity). A systematic parametric study on fuel property influence can only be achieved on the basis of numerical simulations, where single fuel properties can be varied independently. Thus, a unified spray model will be developed, which will be validated over a wide range of fuel properties and which allows a comparatively fast prediction of the temporal spray evolution under Diesel- and Otto-engine relevant conditions. The model will incorporate a new multi-component droplet evaporation model, which is derived in direct collaboration with project IRF-3A-6 (new). The complementary experimental and numerical data will provide essential and well-founded input for the engine experiments.